PROJECT SUMMARY/ABSTRACT HIV presents a major obstacle to human health, particularly in developing nations. The success of HIV is largely due to its ability to adapt to the human host environment and circumvent our innate immune responses. This is principally achieved through viral accessory proteins, which engage cellular proteins to both antagonize host antiviral factors and usurp host cellular machinery. The understanding of these interactions is critical to our fight against HIV. My proposal will determine how cellular proteins involved in the DNA damage response interact with HIV and related lentiviruses to modulate their lifecycle. I hypothesize that the DNA damage response is both anti-viral and pro-viral, as this protein-signaling cascade can sense aberrant DNA and RNA structures and can directly affect cellular homeostasis. HIV belongs to a family of viruses called lentiviruses that infect at least 40 primate species, including humans. Using the natural variation present in lentiviruses, I will determine how Vpr, a viral accessory protein that is common to all extant lentiviruses, has evolved to engage the host DNA damage response through both activation of DNA damage response pathways and direct interactions with DNA damage response proteins. I will specifically test the hypothesis that Vpr directly causes DNA damage in order to activate this cellular response. Furthermore, I will determine if engagement with the DNA damage response is a conserved, and therefore important, function for all lentiviruses, or if it is specific to HIV-1, and thus critical for adaptations and pathogenesis in humans. In addition, I will expand our knowledge of the role of the DNA damage response in lentiviral biology by identifying novel regulators of HIV-1 that are also involved in this cellular response. I will perform an evolution- guided screen to identify candidate DNA damage response proteins and pathways, and I will follow up these hits with specific experiments to elucidate their roles. These studies will identify the DNA damage response as important regulators of HIV-1 and related lentiviruses. They will shed light on lentiviral evolution, on the cellular response to infection, and on the multifaceted roles of the DNA damage response, while helping to identify potential antiviral targets in our fight against HIV.